Magister Scientiae Dentium - MSc(Dent) / The demand for posterior aesthetic restorations has dramatically increased in recent years. Several new materials have been developed with improved aesthetic, adhesive and mechanical properties. However, microleakage elimination, especially if the margins are on dentine or cementum, and attainment of optimum mechanical properties for posterior use, are still questionable. The aim of this study was to investigate microleakage and surface microhardness of a nanofilled, a nanohybrid and an ormocer based nano-ceramic composite restorative material. / South Africa

Magister Scientiae - MSc / Amalgam bonding agents have been shown to enhance retention of amalgam restorations by mechanical means. However, recent studies showed that the use o glass ionomer cements and resin cements as lining and bonding materials to amalgam restorations will increase the retentive strength of the amalgam restorations, hence reducing the micro leakage and secondary caries. The purpose of this study was to compare the relative retentive strength of conventional amalgam restorations and bonded amalgam restorations using resin adhesive, glass ionomer cements and resin cements. / South Africa

Over 200 million dental restorations are performed each year in America. A dental restoration require a strong bonding of restoration to tooth structure and relies on the dental adhesive to create this mechanical and chemical bonding. Dental adhesion or bonding is the process of forming an adhesive joint between the composite and tooth substrate: dentin or enamel. Clinical problems such as microleakage at the restoration tooth interface, influx of fluids, or bacteria growth at the cavity wall can be prevented with adhesives that obtain a more intimate bonding. Longevity of the restoration can be enhanced by the adhesive that creates the tight bonding to reduce problems such as postoperative sensitivity, marginal staining, and recurrent caries. The goal of this research project is to investigate the influence of active scrubbing application as compared to passive non-scrubbing application of the etchant component in 4th generation etch-and-rinse adhesive systems. Shear bond stresses have been measured and compared between application techniques. Verification of resin infiltration depth with each etchant application has been examined with scanning electron microscopy by mounting the etched and bonded enamel surface of the tooth in epoxy and slicing the tooth longitudinally producing a transverse, depth-wise view. Results from this study have clarified the role of resin tag formation as well as tooth morphology during an active acid etchant application for dental restoration.

Indiana University-Purdue University Indianapolis (IUPUI) / Ideal orthodontic springs are able to provide a controlled moment-to-force (M/F) ratio and a low load deflection rate. A great deal of research has gone into describing force systems generated by orthodontic springs. Most studies investigating the force system generated by T-loops have used rigid fixation for the spring ends. This is practical for laboratory studies, but it does not truly represent clinical situations in which orthodontic brackets are used to anchor spring ends. Results from laboratory studies have been applied to clinical situations without regard to what effect, if any, the method of end fixation may have. It is the goal of this study to determine the effects of spring fixation on generated force systems. The springs were held by rigid fixation and bracket ligation with either elastomeric or steel ligature ties. Comparison of these fixation methods was made by testing T-loops of different dimensions, with and without heat treatment at various activation distances. In theory, the wire is ligated rigidly against the bracket, so that the combination acts as a single unit by rigid fixation. Thus, there should be no difference between the generated force systems when spring ends are held by rigid fixation, or when they are held in place with orthodontic brackets and ligated by either elastomeric or steel ligature ties. However, the results indicate that are significant differences among the methods of fixation for each spring variation and heat treatment. The rigid fixation method consistently produced smaller moments and M/F ratios for all springs with every activation and heat treatment combination.

Indiana University-Purdue University Indianapolis (IUPUI) / Direct bonding of orthodontic brackets often results in decalcification of tooth structure surrounding bracket sites. Glass ionomer cements, while typically leaching fluoride over time, often exhibit a significantly lower bond strength. Fluoride-containing resins generally release high concentrations of fluoride for a short time, then cease to release any significant amount. The purpose of this study was to evaluate the tensile bond strength, fluoride release, hardness, solubility, and sorption of a newly formulated fluoride containing resin. The experimental resins were prepared with 5% and 7.5% fluoride (F-) monomer, and were compared to a fluoride-free control adhesive (Rely-a-Bond Phase II™, Reliance Orthodontics Inc ., Itasca, Ill .). To evaluate tensile bond strength, orthodontic brackets were bonded to bovine teeth and debonded using an lnstron machine. Fluoride release was tested using resin disks stored in deionized water. The fluoride content of the water was determined with an ion-specific electrode. Hardness, solubility, and sorption were tested using disks made of each material. Comparison of experimental and control resins by ANOVA followed by General Linear Models multiple comparisons revealed the control to show a statistically significant difference (p<.0001) for tensile bond strength. Experimental Control 5%F- 7.5%F- Peak Stress (MPa) 4.48±0.65 3.83±0.76 5.31±0.97. Fluoride continued to be released from the experimental resins (5% and 7.5% F-) at 18 days. The control was significantly harder than either of the experimental resins at 1 hour, 24 hours, 1 week, and 1 month (p<.0001). The 5% F- resin exhibited slight solubility (0.10 percent), while the 7.5%F- resin and the control exhibited very little solubility (0.01 percent). Phase II™ exhibited significantly lower sorption at 21 days (0.60 percent, p<.001) than either the 5%F- resin (1.69 percent) or the 7.5%F- resin (1.63 percent). These results indicate that while the experimental resin had lower bond strength, lower hardness, and higher sorption than the control, measurable fluoride was released from the experimental resins for up to 18 days. Further testing is indicated to determine the clinical acceptability of this adhesive.

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xi, 56 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 41-44).

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains viii, 107 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 66-71).

Thesis (M.S.)--University of Michigan, 1961.

Thesis (M.S.)--University of Michigan, 1977.

Thesis (M.S.)--University of Michigan, 1984.